Imagine if scientists could use a patient’s own immune system to kill the cancer in their body.

That picture is clearer than you’d think. A team of researchers at the University of Pennsylvania recently sent two patients into total remission from chronic lymphocytic leukemia, and a third into partial remission.

How? Doctors removed a billion of the patient’s T-cells — a type of white blood cell that fights viruses and tumors — and gave them new genes that would program the cells to attack the cancer. Then the altered cells were dripped back into the patient’s veins.

While the two patients are still in remission from the disease, the doctors say that more research needs to be done and that the treatment is still experimental.

We haven’t cured cancer, yet. But the important thing to remember is that progress is made every day by scientists, doctors, and patients participating in clinical trials. This experiment marks the first successful use of gene therapy to train a patient’s own immune system.